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6.3.6. Preserving the Configuration

By default, changes made by the mdadm command only apply to the current session, and will not survive a system restart. At boot time, the mdmonitor service reads the content of the /etc/mdadm.conf configuration file to see which RAID devices to start. If the software RAID was configured during the graphical installation process, this file contains directives listed in Table 6.1, “Common mdadm.conf directives” by default.
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Table 6.1. Common mdadm.conf directives
Option Description
ARRAY
Allows you to identify a particular array.
DEVICE
Allows you to specify a list of devices to scan for a RAID component (for example, “/dev/hda1”). You can also use the keyword partitions to use all partitions listed in /proc/partitions, or containers to specify an array container.
MAILADDR Allows you to specify an email address to use in case of an alert.
To list what ARRAY lines are presently in use regardless of the configuration, run the following command as root: 
mdadm --detail --scan
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Use the output of this command to determine which lines to add to the /etc/mdadm.conf file. You can also display the ARRAY line for a particular device: 
mdadm --detail --brief raid_device
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By redirecting the output of this command, you can add such a line to the configuration file with a single command: 
mdadm --detail --brief raid_device >> /etc/mdadm.conf
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Example 6.6. Preserving the configuration

By default, the /etc/mdadm.conf contains the software RAID configuration created during the system installation: 
# mdadm.conf written out by anaconda
DEVICE partitions
MAILADDR root
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=49c5ac74:c2b79501:5c28cb9c:16a6dd9f
ARRAY /dev/md1 level=raid0 num-devices=2 UUID=76914c11:5bfa2c00:dc6097d1:a1f4506d
ARRAY /dev/md2 level=raid0 num-devices=2 UUID=2b5d38d0:aea898bf:92be20e2:f9d893c5
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Assuming you have created the /dev/md3 device as shown in Example 6.2, “Creating a new RAID device”, you can make it persistent by running the following command: 
~]# mdadm --detail --brief /dev/md3 >> /etc/mdadm.conf
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